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Creating the catalogueCreating the catalogue
Made using the AIPS task VSADMade using the AIPS task VSADVLA Search and DestroyVLA Search and DestroyUsed for the NVSS catalogueUsed for the NVSS catalogueFits a Gaussian to each source in the input Fits a Gaussian to each source in the input
imageimageProduces a source list with fitted parametersProduces a source list with fitted parameters
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SUMSS artifactsSUMSS artifacts
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Pattern matchingPattern matching
Humans are exceptionally good pattern matchersBest example is face recognitionWe have high accuracy and speed
Because we can do it, doesn’t mean we can define what we are doing
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What is Machine Learning?What is Machine Learning?
Any computer system that can change its behaviour when exposed to new data so that it can perform better in the future
Useful when we can’t formulate an algorithmic solution
The classification problem:• Do experts ‘know’ what they are doing?• Wittgenstein’s ‘What is a game?’
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What is a decision tree?What is a decision tree?
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The training/testing processThe training/testing process
We trained C4.5, a decision tree, to classify the We trained C4.5, a decision tree, to classify the potential sources into 3 categories:potential sources into 3 categories:the source is ‘real’the source is an artifactthe source is in a region of low S/N
About 4500 sources were classified by handAbout 4500 sources were classified by hand These were used to train and test the decision These were used to train and test the decision
tree.tree.
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Class 1 or 2: Artefact
Class 3:Genuine
Most genuine sources selected by decision tree here!
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Classification resultsClassification results
Decision TreeDecision Tree
Hum
ansH
umans
AA NN RR
AA 2 1 -
NN - 6 -
RR 2 2 525
Southern section Northern section
We obtained a classification accuracy of ~97%
Decision TreeDecision Tree
Hum
ansH
umans
AA NN RR
AA 16 - 1
NN - 2 -
RR 1 - 333
Reference: Mauch et al., 2003, MNRAS, 342, 1117
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SUMSS artefactsSUMSS artefacts
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SUMSS artefacts - classifiedSUMSS artefacts - classified
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Uniformity of the SUMSS Uniformity of the SUMSS
cataloguecatalogue
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Data productData productCatalogue will cover southern sky with |b|>10o and <-30o.
See: www.astrop.physics.usyd.edu.au/SUMSS/
Flux limit: 6 mJy/beam at dec.<-5010 mJy/beam at dec.>-50
Completeness limit: 8 mJy/beam at dec.<-5018 mJy/beam at dec.>-50
Version 1.6 of catalogue has 200,000 sources above 6 mJy/beam.
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